The SR111 fire was above and behind the cockpit, so correct that cargo fire supression wouldn't have helped. Note that the likely cause of the fire (arcing on a circuit breaker) could happen on twins as well - they use the same CB's
http://www.bst.gc.ca/en/reports/air/...rep3_01_00.asp
777-232LR, your style is better suited to airliners.net than here.